A green car generally includes a high voltage battery for supplying driving power, and an auxiliary battery for supplying operating power to internal electric apparatuses (electronic loads). Here, a low voltage DC-DC converter (LDC) connected to the auxiliary battery and the electric apparatuses down-converts a high voltage of the high voltage battery into a charging voltage of the auxiliary battery when a voltage of the auxiliary battery does not exceed a reference value under the control of an upper controller, thereby charging the auxiliary battery with the charging voltage.
The auxiliary battery serves not only to start the ignition of the vehicle, but also to supply the operating power to the electric apparatuses such as a variety of lamps, a system, electronic control units (ECU), and the like.
Until recently, a lead-acid storage battery has been mainly used as the auxiliary battery of the vehicle because it may be recharged to be used again even when in which it is fully discharged. However, because a lead-acid storage battery is heavy, has low charging density, and particularly because it includes lead-acid, which is an environmental pollutant, lead-acid storage batteries have recently been replaced by lithium ion batteries in green cars.
An apparatus for controlling an auxiliary battery of a green car according to the related art controls a charge/discharge of the auxiliary battery within a fixed usable stage of charge (SoC) range in order to perform the above-mentioned functions. That is, the apparatus for controlling an auxiliary battery of a green car according to the related art controls the LDC to perform the charge when the charge amount of the auxiliary battery decreases to the usable SoC range (e.g., 65% to 95%) or less.
Since the apparatus for controlling an auxiliary battery of a green car according to the related art controls the charge of the auxiliary battery on the basis of the fixed usable SoC range, it needs to frequently perform the charge. The above-mentioned frequent charge increases the consumption amount of power (current) of the high voltage battery that supplies the charging power to the auxiliary battery, thereby resulting in a decrease in fuel efficiency of the vehicle.
In particular, the frequent charging of the auxiliary battery further increases the consumption amount of power of the high voltage battery, when considering loss of energy generated during a process of converting the high voltage of the high voltage battery into a low voltage (e.g., 12 V) for charging the auxiliary battery.